The present invention relates to an ink jet device comprising an ink reservoir and a jetting assembly having at least one printing nozzle.
In an ink jet device, for example an ink jet printer with an ink reservoir and a jetting assembly, the ink reservoir is usually arranged together with the jetting assembly in a printhead which is reciprocated over a printing area. When ink is also stored outside the reciprocating printhead, the printhead usually has an ink supply line for supplying ink to the ink reservoir. For example, in an ink jet printer operating with hot melt ink, i. e. with ink that is solid at room temperature, the ink supply line may comprise an ink melting unit for supplying melted ink to the ink reservoir, and solid ink pellets may be supplied to an open end of the ink melting unit from outside the printhead from time to time. In order to ensure that contaminants are prevented from entering the ink reservoir, an ink filter may be provided at the ink supply line, and the melted ink may be required to flow through the ink filter into the ink reservoir.
Depending on the configuration of the ink jet device, it may be necessary to provide a suction device for applying a negative pressure to an inner space of the ink reservoir to prevent ink from leaking out of the printing nozzles of the jetting assembly. In this case, the ink filter may function as a hydraulic lock, so that the negative pressure can be provided to the ink reservoir while at the same time ink may be supplied to the ink reservoir through the ink filter.
In order to dispose of air bubbles or contaminants that might be present in the jetting assembly, it is desirable to purge the printing nozzles of the jetting assembly from time to time, thereby removing any air bubbles and contaminants. Therefore, a purging device may be provided that is adapted to apply a purging pressure to the inner space of the reservoir for pressing ink into the printing nozzles. However, in case of an ink supply line having an open end, the ink supply line has to be shut off from the ink reservoir to permit the purging device to build up the necessary purging pressure in the ink reservoir.
The necessary purging pressure is usually higher than the absolute value of the negative pressure which is applied to the ink reservoir for preventing ink from leaking ink out of the printing nozzles. In the case of the ink supply line having an ink filter as described above, the ink filter may not function as a hydraulic lock under the comparatively high purging pressure. Thus, a break-through of the ink filter, i.e., an undesired flow of air or ink from the ink reservoir through the ink filter, may take place. In this case, the necessary purging pressure cannot be built up within the ink reservoir.
From U.S. Pat. No. 4,641,154, an ink jet apparatus having a tilt valve that is positioned at an upper wall of the ink reservoir is known. Hot melt ink is melted in an ink melting unit and flows through the tilt valve into the ink reservoir due to gravity. When a purging pressure is to be built up by an ink jet priming system, the tilt valve is moved to a closed position by an actuator. Thus, the tilt valve has to be actively closed in order to enable the ink jet priming system to build up a purging pressure within the ink reservoir. The necessary actuator for closing the valve and the moving parts of the valve which are arranged at the ink supply line are disadvantageous. A further disadvantage results from the fact that the valve is opened by the gravity force of the melted ink as the opening of the valve may be suppressed by capillary forces, i.e., adhesion between the valve element, the liquid ink and the top wall of the reservoir. In such a case, the ink supply line will be blocked.
From U.S. Pat. No. 6,048,057, a hot melt ink jet printhead is known having an ink reservoir with a first chamber and a second chamber. The second chamber comprises a first valve and a second valve. In the normal printing operation of the printhead, ink flows from the first chamber to a nozzle head of the printhead. During a purging operation, a channel between the first chamber and the second chamber is closed, and a channel between the nozzle head and the second chamber is opened. Then, ink flows from the first chamber through the nozzle head into the second chamber. Accordingly, any air bubbles present in the nozzle head are moved into the second chamber. During the normal printing operation, ink is allowed to flow from the second chamber to the first chamber. The valves are arranged at opposite arms of a lever to be alternately closed by a movement of the lever. The lever is activated by an actuating mechanism. A disadvantage is that always one of the valves is in a closed position, so that during printing the ink is not circulated in the chamber between the nozzle head and the second chamber. Moreover, the valves do not shut off the ink supply line from the ink reservoir.
From U.S. Pat. No. 5,489,925, an ink jet printing system is known, wherein a liquid ink supply line extending from a remote liquid ink reservoir to an ink reservoir of a printhead is shut off by a passive check valve. The check valve is spring-biased toward its closed position. The ink reservoir of the printhead may be elevated above the remote reservoir, and ink is supplied through the check valve to the ink reservoir by a pump, thereby opening the check valve. A pressure control system controls the pressure of the ink in the ink reservoir of the printhead to permit purging of air bubbles and contaminants from orifices and passageways. A disadvantage of this ink jet printing system is that a pump is necessary to actively pump the ink through the check valve in the ink supply line.